malformed filename expected %s{version}_x{protocol-version}_

Error message

malformed filename expected %s{version}_x{protocol-version}_{os}_{arch}

What it means

Init() parses a checksum-file entry filename into its components (binary version, protocol version, OS, arch) after stripping the prefix and extension. The remaining name must have at least 4 underscore-separated parts shaped like {prefix}vX.Y.Z_xM.N_os_arch. Fewer parts means the filename does not follow the Packer plugin binary naming convention.

Source

Thrown at packer/plugin-getter/github/getter.go:313

}

// Init method: a file inside will look like so:
//
//	packer-plugin-comment_v0.2.12_x5.0_freebsd_amd64.zip
func (g *Getter) Init(req *plugingetter.Requirement, entry *plugingetter.ChecksumFileEntry) error {
	filename := entry.Filename
	res := strings.TrimPrefix(filename, req.FilenamePrefix())
	// res now looks like v0.2.12_x5.0_freebsd_amd64.zip

	entry.Ext = filepath.Ext(res)

	res = strings.TrimSuffix(res, entry.Ext)
	// res now looks like v0.2.12_x5.0_freebsd_amd64

	parts := strings.Split(res, "_")
	// ["v0.2.12", "x5.0", "freebsd", "amd64"]
	if len(parts) < 4 {
		return fmt.Errorf("malformed filename expected %s{version}_x{protocol-version}_{os}_{arch}", req.FilenamePrefix())
	}

	entry.BinVersion, entry.ProtVersion, entry.Os, entry.Arch = parts[0], parts[1], parts[2], parts[3]

	return nil
}

func (g *Getter) Validate(opt plugingetter.GetOptions, expectedVersion string, installOpts plugingetter.BinaryInstallationOptions, entry *plugingetter.ChecksumFileEntry) error {
	expectedBinVersion := "v" + expectedVersion
	if entry.BinVersion != expectedBinVersion {
		return fmt.Errorf("wrong version: %s does not match expected %s", entry.BinVersion, expectedBinVersion)
	}
	if entry.Os != installOpts.OS || entry.Arch != installOpts.ARCH {
		return fmt.Errorf("wrong system, expected %s_%s", installOpts.OS, installOpts.ARCH)
	}

	return installOpts.CheckProtocolVersion(entry.ProtVersion)
}

View on GitHub (pinned to eb36e3c3e4)

Solutions

Rename the release asset to the standard form: packer-plugin-<name>_<version>_x<protocol>_<os>_<arch>.zip and regenerate the SHA256SUM file.
Rebuild the plugin release with the current packer-plugin-sdk (go build via the SDK scaffolding) so the filename embeds version, protocol, OS, and arch.
Verify the checksums file on the release matches the actual asset names.

Example fix

// before (asset name)
packer-plugin-foo_1.0.0.zip
// after
packer-plugin-foo_1.0.0_x5.0_linux_amd64.zip

Defensive patterns

Strategy: validation

Validate before calling

base := strings.TrimSuffix(strings.TrimPrefix(fname, prefix), ext)
parts := strings.Split(base, "_")
if len(parts) < 4 {
	return fmt.Errorf("asset %q does not match {version}_x{proto}_{os}_{arch}", fname)
}

Type guard

func isWellFormedPluginAsset(fname, prefix, ext string) bool {
	parts := strings.Split(strings.TrimSuffix(strings.TrimPrefix(fname, prefix), ext), "_")
	return len(parts) >= 4 && strings.HasPrefix(parts[1], "x")
}

Try / catch

if err := getter.Init(req, entries); err != nil {
	if strings.Contains(err.Error(), "malformed filename") {
		log.Printf("skipping nonstandard asset: %v", err)
	}
}

Prevention

Publish release assets built by the standard packer-plugin-sdk tooling
Never rename plugin zips by hand
Regenerate the SHA256SUM file whenever asset names change

When it happens

Trigger: Getter.Init() receives a ChecksumFileEntry whose filename, after trimming the prefix (e.g. packer-plugin-), extension (.zip), and splitting on "_", yields fewer than 4 parts — e.g. "packer-plugin-name_v1.0.0.zip" with no _x5.0_linux_amd64 suffix.

Common situations: A hand-rolled or renamed release asset in a GitHub checksums file; a plugin release built with an old or nonstandard naming scheme; a custom/renamed plugin published outside the SDK's naming tooling; corrupted or edited SHA256SUM files.

Understand the failure class

Parsing and encoding errors: unexpected token, malformed input — why parsers reject input and how to find the real culprit.

Related errors

AI-assisted analysis of hashicorp/packer@eb36e3c3e4 (2026-09-05). Data as JSON: /api/errors/81a86f99a25e6861. Report an issue: GitHub.